Makeup artist Michelle Pham made "circle lenses" a YouTube phenomenon, by demonstrating how to use them. So far, she's had nearly ten million hits.

"The contacts are made overseas and are designed to radically change the look of eyes in size and or color," says Pham.

They are hugely popular in Asia with Korean pop stars, and now more Americans are sporting the look.

Chantal George, 19, has bought fourteen pairs of circle lenses over the last three years. Even at $20 to $30 bucks a pop, she says she's hooked.

"It's for the fun of them," she says. "For the same reason I'd pick up a hoodie or a pair of jeans with a crazy design on them. It's an extension of fashion."

It's not that they make her look "prettier", she says. They add a sense of "something interesting."

"It's a conversation starter," she says.

But so-called circle lenses are illegal to sell in the U.S. because they're not FDA approved. And so far no U.S. manufacturer is making them.

Most lenses are manufactured in Asia, purchased online and are widely advertised on Facebook.

But doctors worry the lack of quality control, as with any lens, could result in more eye infections, damage to the cornea, even loss of vision.

"We have no control of where they're manufactured, what their processes are and they're not being fit and appropriately medically cared for by licensed eye doctors," says Dr. S. Barry Eiden, the Chair of the Contact Lens and Cornea Section of the American Optometric Association.

Chantal George says her doctor doesn't know that that she wears the lenses but that she understands the risks.

"That's why you have to go with good brands and good sellers and get from the top of the market, if you can, she says.

But experts warn like anything on the web, what you see, may not be what you get.

"There's nothing wrong with wanting to change eye color as long as its safe and in an approved way under the guidance of a licensed professional," says Eiden.